The invention relates to road paving machines, and more particularly to a an apparatus for tamping paving material before the paving material is leveled by a screed plate on a road paving machine.
Road paving machines are used to deposit, spread, and compact an aggregate-filled tar-based paving material onto a prepared road bed to form a hard pavement surface. Conventional road paving machines include a heavy metal plate called a screed plate that is used to level and compress newly deposited paving material into a compact layer. A typical road paving machine also includes a tamper bar for tamping higher density paving material and distributing the paving material evenly across the screed before the paving material is leveled by the screed.
Tamper bar mechanisms usually include a drive assembly that moves at least one tamper bar into and out of engagement with the paving material to compact the paving material. The drive assembly in some known tamper bar mechanisms drives the tamper bar upward against a biasing force generated by a spring and then disengages from the tamper bar thereby allowing the biasing force of the spring and gravity to drive the tamper bar downward into contact with the paving material.
U.S. Pat. No. 4,828,428 discloses a tamper bar mechanism that includes a drive assembly which drives the tamper bar up and down such that the downward driving force acts through a spring that is coupled between the drive assembly and the tamper bar. The tamper bar is driven downward by the drive assembly until the paving material is compacted to a specific density. When the paving material is compacted to a specific density the forces generated by the drive on the tamper bar overcome the biasing force of the spring causing the spring to compress and the tamper to remain at the same vertical position against the paving material. This configuration compacts the paving material to a desired density determined by the strength of the spring coefficient, but is incapable of compacting the paving material to a desired depth.
The above described mechanisms for tamping paving material are generally effective for compressing and distributing deposited paving material before a screed plate on a road paving machine. Therefore, any improvement in the design or manufacture of such devices for tamping paving material would be desirable.
The present invention is directed to a tamper bar mechanism for tamping paving material and evenly distributing the paving material across a screed plate before the paving material is leveled by a screed plate on a road paving machine.
The tamper bar mechanism of the present invention provides an easily manufactured camshaft that intermittently drives tamper bars into contact with paving material. The camshaft includes one or more individual cams whose profiles determine (i) the speed at which tamper bars move toward the paving material, (ii) the speed at which biasing members move the tamper bars away from the paving material, and (iii) the specific depth to which the tamper bar will compact the paving material. The angular orientations of the individual cams with respect to the other cams on the shaft determine the time at which the driving force is applied to each of the tamper bars. The profiles and the angular orientations of the cams of the tamper bar mechanism are simply modified so that the driving characteristics of the plurality of tamper bars (e.g., speed, depth, timing) can be coordinated to work the paving material in front of the screed according to a desired progression.
The apparatus of the present invention includes a tamper bar for compacting material, a drive, and a biasing member. The drive intermittently forces the tamper bar downward into contact with the paving material at a desired speed and to a desired depth. The biasing member is connected to the tamper bar and biases the tamper bar upward against the drive such that the biasing member raises the tamper bar out of contact with the paving surface after the drive forces the tamper bar downward against the paving material.
In another form, the apparatus includes a plurality of tamper bars for compacting the paving material and a drive connected to the tamper bars. The drive intermittently moves each of the plurality of tamper bars into contact with the paving material at different speeds but preferably similar frequencies to compact the paving material with varying forces across the road paving machine.
The present invention also includes a method for tamping paving material before the paving material is leveled by a screed plate, the method includes: engaging a plurality of tamper bars against a drive; and driving each of the plurality of tamper bars at different speeds.
Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings.